Brothers in arms … Morpurgo’s uncles Pieter Cammaerts, who was killed in the RAF and Pieter’s brother Francis, who worked for the Special Operations Executive.
Composite: Egmont

I have just walked around the ancient ramparts of Ypres, whose name became the byword for stubborn allied resistance against the German invasion of Belgium in 1914 at the beginning of the first world war. It was an invasion that forced 250,000 Belgian refugees to get in boats and seek safety in Britain. They came. They were welcomed. They were cared for. This should be remembered, perhaps, as a lesson in kindness for us today.

In the evening, I stood in the bitter cold under the Menin Gate as the Ypres fire brigade bugles played the Last Post, as they have done every evening since 1928, except during the German occupation of Belgium in the second world war. As the echoes faded, I thought of my uncle Pieter Cammaerts, who died in the second world war – in the RAF, aged 21, in 1941. Uncle Pieter is buried in the church at Radlett, his name is on the war memorial in the Hertfordshire town, but almost no one alive today knew him. He died two years before I was born and I know him only from photographs, from family stories. But so much of the reason I was standing under the gate, so much of why I had written my most recent book, In the Mouth of the Wolf, and War Horse and Private Peaceful, was because of my uncle Pieter, and my uncle Francis.

My uncles have fascinated and inspired me since I was a child. In my family, their lives are legendary. All my writing life I had wanted to tell their story. Writing it was my way of trying to remember them, of acknowledging my debt to them, and all the millions of “mouthless dead” of two wars. They had fought for peace. I had enjoyed that peace in a Europe that, for the most part, had decided enough was enough, that war was not the way. I lived in a European Union. We members argued often, but no longer fought. Togetherness seemed to be working. Peace had become too precious. My uncles were among those who had enabled that reconciliation to happen.

The two brothers, though very different – Francis, tall, confident and charismatic, Pieter, smaller, tentative and fragile – were close. They came from a Christian socialist family, their father, Emile, was a Belgian poet and free thinker, later art critic, philosopher and professor of Belgian studies at London University. Their mother, Tita, was an actor, a devoted Christian, a formidable and highly principled woman. There were four equally formidable sisters, my mother among them. It was a house of music, theatre and books, of heated discussion and strong opinions. Holidays were often spent walking in the Ardennes, which the family loved.

Francis, a socialist and pacifist, went to Cambridge and became a teacher. Pieter went to Rada in London and was starting out on a promising career as an actor when war broke out in September 1939. He joined up almost at once. Francis, following his convictions, became a conscientious objector, and was sent to work as a shepherd on a Lincolnshire farm. The Germans were soon invading Belgium, through the family’s beloved Ardennes, and marching into France, towards the Channel. Invasion was threatening.

Francis walked into a room in Baker Street a shepherd, and came out an officer in the Special Operations Executive

In 1941, Pieter, now a sergeant observer in the RAF, was killed when his plane crashed in St Eval in Cornwall. The family were devastated. Francis, still shepherding but now a husband and father, decided he could no longer stand by while others were fighting for his family’s survival, and for the beliefs and freedoms that were so precious to him.

He confided his dilemma to Harry Rée, his great friend, fellow teacher and pacifist, who, unbeknown to Francis, had already joined the Special Operations Executive, SOE. Francis spoke fluent French. Harry said that could be useful, and that he would put him in touch with someone in London. Francis walked into an interview in an upstairs room in Baker Street a shepherd, and came out an officer in the SOE.

After months of gruelling training, during which he could say nothing to his wife, Nan, or his friends and family, Francis found himself in German occupied France. In Paris, he realised at once that fellow agents there were compromised. Within days more than 60 were rounded up and shot. Francis by this time had made his way south, where he found himself organising and supplying resistance fighters, the Maquis, across a swath of southern France, an army that in the end numbered more than 10,000 men and women, comprising communists, socialists and Gaullists, from all walks of life, all determined to rid their country of the invader.

So this pacifist uncle was now a secret agent, fighting the enemy, living in constant danger of capture and death. But he proved to be an agent who had all the right instincts. Trust, he knew, was everything. He had seen others’ mistakes. He picked his few friends with great care. He was courageous, and scrupulous about security, never sleeping more than two nights in one place. He inspired and gave great loyalty.

The Germans put a huge price on his head, but he was never betrayed. He managed to outwit both the Gestapo and their counterparts in the dreaded French Milice, and survived these perilous years through his skill and bravery, but also through the love and courage of his comrades. He returned after the liberation of France to his family, and to his life as a headteacher, and a principal of teacher-training colleges in England and in Botswana.

When Francis was an old man, I visited him in Le Pouget, the village in south-east France where he came to live in his latter years, to be closer to his family and his old friends from the resistance. Only if pressed would he speak of his war years. Two weeks before he died, the villagers gave him a 90th birthday party. The children sang, the mayor made a speech. He was a legend there, too, not only in his family.

More and more I wanted to tell his story. It was important to the family and to me, especially now Britain had decided to leave the European Union.

The Mouth of the Wolf begins with an old Englishman being given a 90th birthday party by the people of his French village. Tired, he goes to bed and remembers those people who could not be there with him that day. He talks to them, remembers with them the joys and the sorrows. But it was difficult, I found, to settle to my writing in the midst of the post-referendum furore.

It came to me as I was trying to weave the story of my two uncles, that in all the bitter bickering about Europe, few if any were talking about why the EU was there, how it came to be. My uncles had done what they had done to defeat tyranny, to bring peace and reconciliation. They knew, we all know, that for hundreds of years, thousands even, European states had fought one another. Trade wars, religious wars, power grabs, land grabs, disputes between kings and emperors – our continent has been almost constantly at war over the centuries.

In the last century, the inclination of the great European powers towards belligerence and self-destruction led us into the two most destructive wars the world has ever known. Then, out of the rubble, out of all the grieving and misery, France and Germany, the two great nations at the heart of these titanic struggles, decided that the only way to ensure peace was through trade; that if they created close, mutually beneficial links, there would never be any need or wish to fight, that prosperity, security and peace would be interlocked.

Soon, six nations gathered together to create this trading bloc. Europe’s peoples could see the sense of this. More wanted to join. So the new Europe, changing its name and much else besides, grew in numbers, grew closer, and did help to bring lasting peace. But it became bureaucratic, less democratic, put ever more stars on its flag, and created a new currency. The mutual benefits of prosperity and stability were evident, but were not shared equitably. We were a member of a club in which we felt we were losing control over our destiny, where the rules were being changed, which alarmed many. We argued, all the countries argued. But it was still jaw-jaw, not war-war.

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In this febrile atmosphere came the referendum. I was sure the people would vote to stay in because I thought British people valued peace above all else, and the prosperity most had enjoyed for so long. Yes, there was plenty we did not like about Europe, but we would stay and put that right.

I was wrong. But I am sure, too, that the country was wrong, deluded by lies and statistics, by absurd promises. I feel we are now travelling down a path that takes us away from our friends and neighbours. We have told them we don’t like them, that we wish to divorce them. They are hurt, upset, angry. Why wouldn’t they be?

My uncles’ lives taught me that peace must come first, before prosperity. They helped make Europe a place of peace at last, of free peoples. That’s the Europe, with all its faults, I believe we belong to. That Channel of ours has saved us in the past, often. Now it threatens to separate us. Holding hands across the sea is the only way. It always was. My uncles knew that.

• In the Mouth of the Wolf is published by Egmont. To order a copy for £11.04 (RRP £12.99) go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99.